i have a v8 discovery auto and I get at least 150 miles off 50 liters even when I'm driving it hard.. and it's only single point... so I would agree there's a problem but sorry can't help with what the problem is... presumably you've checked the obvious - ie what's the fuel consumption like on petrol... are your brakes seized, have you done oil and filter, air filter (mine's minging - must get round to sorting that) is it running smoothly or does it need a tune etc etc